The present invention relates generally to UV treatment systems and specifically to systems and methods for achieving flame restrictive seals in such systems. To achieve EX-D compliance, conventional systems require large enclosures be used to house and connect various components (e.g. UV probes) to UV treatment reactors. The present invention allows a smaller enclosure to be used by providing a single retainer that engages the threaded portions of a body and cap. The threaded portions thereof having sufficient thread pitch and length to achieve a compliant flame path.